Cellulitis (sel-u-LIE-tis) is a common, potentially serious bacterial skin infection. Cellulitis appears as a swollen, red area of skin that feels hot and tender. It can spread rapidly to other parts of the body. Cellulitis isn't usually spread from person to person.

Skin on lower legs is most commonly affected, though cellulitis can occur anywhere on your body or face. Cellulitis might affect only your skin's surface. Or it might also affect tissues underlying your skin and can spread to your lymph nodes and bloodstream.

Left untreated, the spreading infection can rapidly turn life-threatening. It's important to seek immediate medical attention if cellulitis symptoms occur.

Possible signs and symptoms of cellulitis, which usually occur on one side of the body, include:

Red area of skin that tends to expand

Swelling

Tenderness

Pain

Warmth

Fever

Red spots

Blisters

Skin dimpling

When to see a doctor

It's important to identify and treat cellulitis early because the condition can spread rapidly throughout your body.

Seek emergency care if:

You have a red, swollen, tender rash or a rash that's changing rapidly

You have a fever

See your doctor, preferably that day, if:

You have a rash that's red, swollen, tender and warm — and it's expanding — but without fever

Cellulitis occurs when bacteria, most commonly streptococcus and staphylococcus, enter through a crack or break in your skin. The incidence of a more serious staphylococcus infection called methicillin-resistant Staphylococcus aureus (MRSA) is increasing.

Although cellulitis can occur anywhere on your body, the most common location is the lower leg. Bacteria is most likely to enter disrupted areas of skin, such as where you've had recent surgery, cuts, puncture wounds, an ulcer, athlete's foot or dermatitis.

Certain types of insect or spider bites also can transmit the bacteria that start the infection. Bacteria can also enter through areas of dry, flaky skin or swollen skin.

Several factors can place you at greater risk of developing cellulitis:

Weakened immune system. Conditions that weaken your immune system — such as diabetes, leukemia and HIV/AIDS — leave you more susceptible to infections. Certain medications, such as corticosteroids, also can weaken your immune system.

Skin conditions. Skin disorders — such as eczema, athlete's foot, chickenpox and shingles — can cause breaks in the skin and give bacteria an entry point.

History of cellulitis. People who previously had cellulitis, especially of the lower leg, may be more prone to develop it again.

Intravenous drug use. People who inject illegal drugs have a higher risk of developing cellulitis.

Obesity. Being overweight or obese increases your risk of developing cellulitis and having recurring episodes.

The bacteria that cause cellulitis can spread rapidly, entering lymph nodes and your bloodstream. Recurrent episodes of cellulitis may damage the lymphatic drainage system and cause chronic swelling of the affected limb.

In rare cases, the infection can spread to the deep layer of tissue called the fascial lining. Flesh-eating strep (necrotizing fasciitis) is an example of a deep-layer infection. It represents an extreme emergency.

You're likely to start by seeing your family doctor or a general practitioner, who may refer you to a doctor who specializes in skin disorders (dermatologist). If you have a severe infection, an emergency room doctor may examine you first. You may also be referred to an infectious disease specialist.

Here's some information to help you get ready for your appointment.

What you can do

List your symptoms, including any that may seem unrelated to the reason for which you scheduled the appointment.

List key personal information, such as if you've had any recent surgeries, injuries, animal bites or insect bites.

List medications, vitamins and supplements you're taking and the dosage.

List questions to ask your doctor.

Preparing a list of questions can help you make sure that you cover the points that are important to you. For cellulitis, some basic questions to ask your doctor include:

How might I have gotten this infection?

What tests do I need? Do these tests require special preparation?

How is this treated?

How long before the treatment starts working?

What side effects are possible with this medication?

I have other medical conditions. How do I manage them together?

Are there alternatives to antibiotics?

Is there a generic alternative to the medicine you're prescribing?

How can I prevent this type of infection in the future?

Do you have any brochures or other printed material that I can have? What websites do you recommend?

Don't hesitate to ask other questions you have.

What to expect from your doctor

Your doctor is likely to ask you a number of questions, such as:

When did your symptoms start?

Do you remember injuries or insect bites to that area?

How severe is the pain?

Does anything seem to improve your symptoms?

Are you allergic to or intolerant of any antibiotics?

Have you had this type of infection before?

What you can do in the meantime

You may need a prescription antibiotic to clear your infection. However, until you see your doctor, you can wash the injured area with soap and water and place a cool, damp cloth over the affected area for relief.

Your skin's appearance will help your doctor make a diagnosis. He or she may also suggest blood tests, a wound culture or other tests to help rule out other conditions.

Cellulitis treatment usually includes a prescription oral antibiotic. Within three days of starting an antibiotic, let your doctor know whether the infection is responding to treatment. You'll need to take the antibiotic for as long as your doctor directs, usually five to 10 days but possibly as long as 14 days.

In most cases, signs and symptoms of cellulitis disappear after a few days. You may need to be hospitalized and receive antibiotics through your veins (intravenously) if:

Signs and symptoms don't respond to oral antibiotics

Signs and symptoms are extensive

You have a high fever

Usually, doctors prescribe a drug that's effective against both streptococci and staphylococci. It's important that you take the medication as directed and finish the entire course of medication, even after you feel better.

Your doctor also might recommend elevating the affected area, which may speed recovery.

If your cellulitis recurs, your doctor may recommend preventive antibiotics. To help prevent cellulitis and other infections, take these precautions when you have a skin wound:

Wash your wound daily with soap and water. Do this gently as part of your normal bathing.

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